The present invention relates to a process for producing a cross-linked granular polyarylene sulfide by reacting a metal sulfide, a dihaloaromatic compound and a polyhaloaromatic compound in an organic amide solvent, comprising:
(1) an initial-stage polymerization step (A) for preparing a polyarylene sulfide of a low melt viscosity;
(2) a temperature raising step (B); and
(3) a second-stage polymerization step (C),
wherein the ratio of water to the metal sulfide, the reaction temperature and the temperature increasing rate are regulated according to the necessity. The invention also relates to a cross-linked granular polyarylene sulfide produced by the process.
As a typical method to produce a polyarylene sulfide (hereinafter referred to as "PAS"), for example, polyphenylene sulfide, a process comprising reacting an aromatic compound having at least one halogen substituents, such as a dihaloaromatic compound, and an alkali metal sulfide in an organic amide solvent such as N-methylpyrrolidone is disclosed in U.S. Pat. No. 3,524,835.
Although cross-linked PAS can be produced even with this process, since the obtained polymer is fine powders of not more than 50 .mu.m in an average particle diameter, the recovery, washing and drying of said polymer are not easy and handling of the polymer is troublesome since the polymer prone to scatter during a molding work or to cause blocking in a hopper.
Methods to obtain PAS in a granular form by allowing an appropriate amount of water to exist during or after polymerization step, are disclosed in U.S. Pat. Nos. 3,919,177; 4,645,826 and 4,745,167, European Patents 244,187 and 256,757 and Japanese Patent Application Laid-Open (KOKAI) No. 62-285,922 (1987). However, when it is tried to produce highly cross-linked PAS by reacting a dihaloaromatic compound mixed with a polyhaloaromatic compound, which has more than 2 halogen substituents in a molecule, with an alkali metal sulfide, it is prone to form large masses of agglomerated particles of PAS during polymerization and cause some difficulties in handling.
As a method to obtain granular PAS having relatively high melt viscosity, for instance, several thousands to several ten thousands of poise measured at 310.degree. C. and a shear rate of 1,200/second, U.S. Pat. No. 4,794,164 discloses a two-stage polymerization method in which the second-stage polymerization is conducted at a high temperature in the range of 245.degree. and 290.degree. C., the temperature of last half of the second-stage is lowered to 220.degree. to 250.degree. C. and the temperature is maintained at the level for a predetermined period of time and thereafter continue the polymerization at a temperature and for a period of time determined according to necessity. However, this method also has a possibility to form large masses of agglomerated particles of PAS during polymerization in case of producing such highly cross-linked PAS as the present invention, therefore the commercial production of this type of PAS by this method is not always easy.
Further, U.S. Pat. No. 4,116,947 discloses a method to produce a branched PAS, having low melt flow value sufficient to be molded without any prior curing, by using dihaloaromatic compound(s) and at least one kind of polyhaloaromatic compound having more than two halogen substituents in a molecule, in the presence of a small amount of water. Although the obtained PAS by the method is thought to have enough melt viscosity to be molded, the method is different from the one to produce granular PAS of high melt viscosity of the present invention.
Taking into consideration the above, the present inventors have extensively studied a mechanism to form granular polymer during polymerization, aiming to obtain a high cross-linked PAS having high melt viscosity, which becomes gel under melting, in a form of granules which is easy to handle thereafter.
The present inventors have further promoted the results obtained and attained the present invention.